1. Field of the Invention
This invention relates generally to wafer fabrication processes, and, more particularly, to a method and apparatus for controlling film thickness uniformity of a plurality of wafers processed by a multi-zone furnace.
2. Description of the Related Art
There is a constant drive in the semiconductor industry to increase the quality, reliability, and throughput of integrated circuit devices such as microprocessors, memory devices and the like. This drive is fueled by consumer demands for higher quality computers and electronic devices that operate more reliably.
These demands by the consumer have resulted in some improvements in the manufacture of semiconductor devices. Reducing defects in the manufacture of these devices lowers the cost of the devices themselves. Accordingly, the cost of the final product incorporating these devices is also reduced, thus providing inherent monetary benefits to both the consumer and manufacturer.
During the course of manufacturing semiconductor devices, wafers may be subjected to one or more heating or baking operations for a variety of reasons. For example, wafers may be subjected to such heating during thermal oxidation processes used to form a layer of silicon dioxide on the wafer. Typically, however, problems are encountered with such heating or baking processes conducted with the wafer. Generally, the wafers are loaded into a multi-zone vertical furnace and are baked by the furnace at a particular temperature for a specified baking time. Usually, the actual temperature within each of the zones will vary from one zone to another within the furnace. The temperature variation between the zones may result because heat from the bottom of the vertical furnace rises to the top, thereby causing the zones near the top of the furnace to be hotter than the zones towards the bottom of the furnace. Additionally, various other factors generally cause variations in temperature between the zones of the furnace, such as the gas flow within the furnace, for example.
When the actual temperature of each zone of the furnace differs, a variation of film thickness between the wafers may undesirably result within the batch of wafers processed by the furnace. Such a variation in film thickness between the wafers may cause defects in these wafers while being processed further down the semiconductor processing line, thereby increasing costs for the manufacturer, and, ultimately, the consumer. For example, if the layers produced on the wafer by the furnace are thicker than anticipated due to a locally increased temperature within a zone of the furnace, subsequent etching processes may not remove all of the layer of material. This may lend to costly rework of the wafers and reduce manufacturing efficiencies.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.